A statistical approach to predict the failure enthalpy and reliability of irradiated pwr fuel rods during reactivity-initiated accidents

During the last decade, the failure behavior of high-burnup fuel rods under a reactivity-initiated accident (RIA) condition has been a serious concern since fuel rod failures at low enthalpy have been observed. This has resul ted in the reassessment of existing licensing criteria and failure-mode stu dy. To address the issue, a statistics-based methodology is suggested to pr edict failure probability of irradiated fuel rods under an RIA. Based on RI A simulation results in the literature, a failure enthalpy correlation for an irradiated fuel rod is constructed as a function of oxide thickness, fue l burnup, and pulse width. Using the failure enthalpy correlation, a new co ncept of "equivalent enthalpy" is introduced to reflect the effects of the three primary factors as well as peak fuel enthalpy into a single damage pa rameter. Moreover, the failure distribution function with equivalent enthal py is derived, applying a two-parameter Weibull statistical model. Finally, the sensitivity analysis is carried out to estimate the effects of burnup, corrosion, peak fuel enthalpy, pulse width, and cladding materials used.